1. Field of the Invention
The invention relates to a process for soldering an electric connector onto a circuit board. More particularly, the invention relates to a process of soldering an electric connector onto a circuit board with increased yield and soldering reliability and reduced production cost.
2. Description of the Related Art
Bonding techniques used to attach an electric connector onto a circuit board include Direct Insertion Pin (DIP), Surface Mount Technology , and Ball Grid Array (BGA). However, these different bonding techniques may have some disadvantages.
Referring to FIG. 1 and FIG. 2, an electric connector 1 and a circuit board 2 are bonded to each other by the DIP technique. A plurality of leads 3 of the electric connector 1 respectively penetrate a plurality of through holes 4 of the circuit board 2 and then a solder paste is dispensed over the through holes 4, formed by drilling the circuit board 2. The through holes 4 adversely affect the high integrity of circuit design, especially in the case of multi-layered routing. Therefore, the size of the circuit board 2 and the electric connector 3 cannot be desirably reduced.
Referring to FIG. 3 and FIG. 4, an electric connector 5 and a circuit board 7 are bonded to each other by SMT. Each lead 6 of the electric connector 5 is bent to form a contact portion 8 parallel to the circuit board 7. The contact portion 8 is attached to a solder paste 9 dispensed over the circuit board 7. An infrared radiation (IR) or hot air flow is used to bond the electric connector 5 to the circuit board 7. In SMT, a flux in the solder paste 9 removes an oxide layer on a top of each contact portion 8 facing the solder paste 9 when the soldering temperature exceeds about 150xc2x0 C. As the temperature rises, the flux evaporates. At about 187xc2x0 C., fine tin particles in the solder paste 9 begin melting and bond with the contact portions 8. One disadvantage of SMT is that when the circuit board 7 or the electric connector 5 is slightly bent or the contact portions 8 are not at the same level, some of the contact portions 8 cannot touch the solder paste 9. When the solder paste 9 is heated, these contact portions 8 are not dipped in a flux of the solder paste 9, which causes soldering defects. Furthermore, an oxide layer is often formed over the contact portions 8, which raises the whole resistance thereof and may even cause a soldering failure of the contact portions 8. The above disadvantages adversely affect the performance of the electric connector 5.
As the amount of leads on the electric connector increases, it becomes more difficult to control the yield. Therefore, a BGA bonding process is proposed.
Referring to FIG. 5 and FIG. 6, an electric connector 13 and a circuit board 12 are bonded to each other by BGA process. The solder ball 11 is placed on a terminal of each lead 10. During heating, if the circuit board 12 or the electric connector 13 is slightly bent or the solder balls 11 are not of a same height, the solder ball 11 at a higher level cannot be dipped in the flux within in a solder paste 14. On the other hand, the solder ball 11 at a lower level tends to be deformed after being heated. Deformation of the solder ball 11 lowers the overall position of the solder balls 11, which reduces soldering failure of the contacts portions. However, soldering the solder balls 11 on the terminals of the lead 10 needs is expensive and time-consuming.
In both SMT and BGA techniques, the respective contact areas of the solder paste and the circuit board are so large that the solder paste at the tip of each lead tends to spread out and contact with other solder paste areas, causing a short circuit.
It is therefore an object of the invention to provide a process for soldering an electric connector on a circuit board, which process increases yield and soldering reliability and reduces production cost.
In order to achieve the above and other objectives, a process for soldering an electric connector on a circuit board is provided. The connector includes an insulator and a plurality of leads mounted inside the insulator. Each lead has a first end extending into a soldering terminal to a bonding surface of the insulator. A soft solder paste is dispensed over a bonding surface of the circuit board. The soldering process includes the following steps: a) inserting the soldering terminal of each lead in the soft solder paste; and b) applying heat to the soft solder paste to bond the soldering terminal and the circuit board together.
The soldering terminal of the lead is directly inserted into the soft solder paste on. the circuit board and then fixedly bonded by heating. The circuit board therefore does not need to be drilled for external bonding to the electric connector. The direct insertion of the soldering terminal of the lead into the soft solder paste on the circuit board minimizes the contact area between the lead and the circuit board and prevents the solder paste from being unduly spread, which would cause a short circuit. Furthermore, the yield and soldering reliability are increased while the production cost is reduced.
To provide a further understanding of the invention, the following detailed description illustrates embodiments and examples of the invention, this detailed description being provided only for illustration of the invention.